The major objective of this research proposal is to investigate the role of the trk family of tyrosine kinase receptors, which have been identified as specific receptors for neurotrophins, in the maturation of the central nervous system (CNS) and in its response to injury. These experiments will use an in vivo experimental approach to evaluate the interactions between specific neurotrophins (NGF, BDNF, and NT-3) and the trk family of receptors (trkA, trkB, and trkC) that are present in the forebrain and mesencephalon of postnatal and adult rodents. Immunohistochemical procedures, immunoprecipitation assays, in situ hybridization techniques, and RNase protection assays will be used to address four specific aims. the first aim is to identify the neurotrophin receptor that is present in mature astrocytes. These studies will use the optic nerve as an in vivo experimental preparation for identifying which trk receptor subtype is present in mature astrocytes and for characterizing its phosphorylation in response to NGF, BDNF, and NT-3. In the second specific aim the postnatal expression of the neurotrophin receptors will be characterized in both neuronal and glial cells and the distribution of these cell populations will be compared with that observed in the adult CNS. These experiments will determine which subtype of receptor (trkA, trkB or trkC) is present on a specific neuronal phenotype. Aim three will investigate the effects of intraventricular and intraparenchymal injections of NGF, BDNF, and NT- 3 on trk receptors. The proposed studies will concentrate on evaluating trophic factor-receptor interactions that occur in the septohippocampal and nigrostriatal systems. A dose response and time course for the selective activation of trk receptors by the different neurotrophins will be determined in postnatal and adult rats. In additional experiments, priming doses of neurotrophins will be used to evaluate whether the administration of a specific trophic factor alters the expression of its receptor. The experiments in specific aim four will concentrate on evaluating lesion induced changes in the expression of the different trk receptor subtypes in the septohippocampal and nigrostriatal systems. The effects of both mechanical axotomy and excitotoxic lesions will be evaluated in immature and adult animals. It is anticipated that the proposed experiments will provide novel and important basic scientific information that will contribute toward our understanding of the possible role that neurotrophin receptors may play during the maturation of the CNS and in its response to injury.